Antifriction bearing

ABSTRACT

The present invention relates to the antifriction bearings used, in particular, on railway transport. The invention consists in that the races and rolling elements of the bearing have a constant chemical composition of steel throughout their volume with a carbon content of 0.8 - 1.2 percent and have a hardened layer at least on the rolling surfaces with a hardness of 58 - 65 HRC, the depth of this layer being 0.1 - 0.3 of the wall thickness of the race, and hardened to 30 - 45 HRC. The invention also claims a method of heat treatment of the races and rolling elements wherein surface hardening is carried out by a single through heating to temperatures above AI and by intensive cooling.

United States Patent Shepelyakovsky et al.

[ 51 Aug. 8, 1972 [54] ANTIFRICTION BEARING Assignee: Moskovsky VechernyMetallurgishesky lnstitut, Moscow, U.S.S.R.

Filed: July 15, 1970 Appl. No.: 55,100

US. Cl ..308/212 Int. Cl. ..Fl6c 32/22 Field of Search ..308/241, 187,193, 195, 008

[56] References Cited FOREIGN PATENTS 0R APPLlCATlONS 544,247 4/ 1942Great Britain ..308/008 Primary Examiner-Martin P. Schwadron AssistantExaminer-Frank Susko Attorney-Waters, Roditi, Schwartz & Nissen [57]ABSTRACT The present invention relates to the antifriction bearingsused, in particular, on railway transport.

The invention consists in that the races and rolling elements of thebearing have a constant chemical composition of steel throughout theirvolume with a carbon content of 0.8 1.2 percent and have a hardenedlayer at least on the rolling surfaces with a hardness of 58 65 HRC, thedepth of this layer being 0.1 0.3 of the wall thickness of the race, andhardened to 30 45 HRC.

The invention also claims a method of heat treatment of the races androlling elements wherein surface hardening is carried out by a singlethrough heating to temperatures above A, and by intensive cooling.

4 Claims, 2 Drawing Figures ANTIFRICTION BEARING The present inventionrelates to antifriction bearings used in particular, in railway rollingstock.

While in operation, the bearing races and rolling elements are subjectedto heavy contact, impact and static loads. Therefore, they shouldpossess a high resistance to contact stresses combined with sufiicientstrength.

At present, the antifriction bearings are manufactured according to twomethods.

In the first method the bearings are made of alloy steel with 0.9 1.1percent carbon. The bearing races and rolling elements are hardened bythrough heating, and tempered at a low temperature. This type of heattreatment produces an identical hardness of the races and rollingelements across the entire section, this hardness ranging from 58 to 64HRC. This results in an unfavorable distribution of internal residualstresses in the bearing races and rolling elements and in a highsensitivity to various concentrations of stresses (nonmetallicinclusions, grinding burns, notches, etc.). This impairs sharply thereliability of the bearings.

1n the second method the bearings are made of lowcarbon alloy steels.The races and rolling elements are case-hardened 1.0 3.0 mm deep,normalized or annealed, then hardened and tempered at a low temperature.After such a heat treatment the hardness the races and rolling elementsvaries from 58 to 64 R in the case-hardened surface layer, dropping to30 45 HRC in the core. This method of bearing manufacture calls for avery long case-hardening process (in excess of hours), expensive andbulky equipment and some means of regulating the process. All thisinevitably brings about a raise in the cost of the bearings.

It is an object of the present invention to provide an antifrictionbearing which would feature higher structural strength, reliability inoperation and durability as compared to the prior art bearing. Anotherobject of the present invention is to provide an antifriction bearingmanufactured from less expensive steel, as ultra pure electroslagrefined steel is not required.

Still another object of the present invention is to provide a method ofheat treatment for the races and rolling elements which would be lessdurable and less labor-consuming in comparison with exisling.

Other objects and advantages of the present invention will be apparentfrom the following description.

These and other objects are accomplished by providing a bearingcomprising races with rolling elements between them wherein, accordingto the invention, the races and rolling elements have a constantchemical composition of steel throughout their volume, the hardenabilityof said steel being confined at the maximum and minimum limits tosatisfy the relation d (0.7 1.4).? where S thickness of race wall, dcritical diameter, i.e. the diameter of a cylindrical specimen of thissteel, hardened by through heating and rapid cooling (for example by ahigh speed water shower) to a hardness of 55 HRC, in the center theseraces having a hardened layer with a hardness of 58 65 R the depth ofthe hardened layer constituting0.l 0.3 of the race wall thickness, withthe core hardened to 30 45 HRC.

This method also ensures that the races and rolling elements should havea hardened layer over the entire surface.

The races and rolling elements may be made of steel containing 0.9 1.1percent carbon, 0.3 0.5 percent chromium, 0.1 0.3 percent silicon, and0.1 0.3 percent manganese.

The races and rolling elements may also be made of steel containing 0.91.1 percent carbon, 0.4 0.6 percent chromium, not over 0.1 percentsilicon and 0.1 0.3 percent manganese.

For manufacturing said bearings we hereby propose a method of heattreatment of the races and rolling elements wherein, according to theinvention, the races and rolling elements are surface hardened by asingle through heating to temperatures above A,, and by intensivecooling.

It is expedient that the hardened races and rolling elements beintensively cooled with high speed shower or stream of water.

After hardening, the races and rolling elements are subjected to alow-temperature tempering. This may take the form either ofself-tempering by the heat remaining in the hardened race or rollingelement in case of incomplete cooling, or by additional tempering in afurnace.

Due to regulated upper and lower limits of steel hardenability, thesurface of the hardened races and rolling elements asquires a martensitelayer whose depth is 0.1 0.3 of the race thickness, hardness 63 67 HRC,while their deeper parts have a structure of fine-grainedferrite-cementite mixture of the troos titic or sorbitic type with ahardness of 30 45 HRC depending on the size of the races and rollingelements. The core hardness of the races or rolling elements rises withthe decrease of of their thickness. In the races whose wall thickness isabout I5 mm, the martensite layer is 2.5 3.5 mm thick. In this casecarburizing is not required. After tempering at I50 C., the surfacehardness is in the range from 62 to 64 HRC. Such distribution of harnessacross the section of the races and rolling elements of a bearingensures a favorable distribution of residual internal stresses, andcreates internal compressive stresses in the surface layers whichimproves fatigue strength and reduces the sensitivity of the races androlling elements to concentrations of stresses. A high surface hardnessof the races and rolling elements with the above-specified carboncontent ensures their high contact strength while a reduced content ofresidual austenite and a lower degree of alloying of steel increase thestability of their dimensions.

Usually, steels with 0.8 1.2 percent carbon content are protectedagainst cracking during hardening by oil quenching which restricts thehardness of steel to a certain extent after hardening. Contrary to theprevailing practice, we propose that steels with the abovespecifiedcarbon content and regilated hardenability, should be surface-hardenedby through heating and cooling with an intensive shower or stream ofwater.

The races and rolling elements hardened by this method and made of theabove-specified steel are harder by 3 4 Rockwell units than theoil-quenched ones and are completely devoid of cracks.

The realization of the present invention increases the structuralstrength, operational reliability and durability of the antifrictionbearing along with a substantial decrease of its cost due to a reductionin the degree of steel aloying, in the duration of heat treatment andamount of labor involved in heat treatment, and owing to smallergrinding allowances for the races and rolling elements. Besides, apossibility presents itself of automating the process of heat treatmentof the bearing races and rolling elements directly in the productionline.

Now the invention will be described by way of example with reference tothe drawings, in which:

FIG. I is a cross section of antifriction box bearing for railway carsrealized in accordance with the invention, illustrating themacrostructure of races and rolling elements;

F IG. 2 is a section taken along line lI--ll in FIG. 1.

The roller bearing for railway car axle boxes comprises an outer race 1(FIGS. 1, 2), an inner race 2 with rollers 3 between them, and a cage 4.The outer race I is installed rigidly in the seat (not shown), the innerrace is press-fitted on the wheel axle (not shown). The inner and outerraces and rollers are subjected to heavy contact stresses in operation.Besides, the bearing suffers impact loads originated by wheels strikingrall rail joint, etc. Therefore, along with a high contact strength, theraces and rollers should resist impact loads and have a high bendingstrength.

These requirements are satisfied by the bearing whose races and rollingelements are made of steel with regulated upper and lower hardenabilitylimits, containing 1.0 percent carbon, 0.4 percent chromium, 0.22percent silicon, 0.22 percent manganese. The hardness of the surfacelayer is 62 64 l-lRC 2.5 3.5 mm in depth. This'hardness graduallydecreases to 35 45 HRC from the surface towards the core.

The method of heat treatment of races and rollers made ofabove-specified steel and producing nonuniform hardness across theirsection consists in hardening them by through induction heating to 830850 C. with intensive all-round cooling by a high speed shower or streamof water, followed by tempering at 150 180 C.

This heat treatment produces a layer of martensite 2.5 3.5 mm deep onthe entire surface of the races and rollers this layer having a hardnessof 62 64 HRC; the layer of martensite is followed by troostite andtrostosorbite, so that the hardness is gradually reduced from themartensite layer towards the core, reaching 35 45 HRC. A high surfacehardness with a carbon content of 1 percent ensures a high contactstrength while the combination of the hard surface layer with a toughcore, the residual internal compressive stresses at the surface being 6080 kg/mm produces a high fatigue strength and a low sensitivity to theconcentrations of stress.

The results of tests (see Table) have shown that the resistance torolling contact loads of the proposed races is 1.5 2 times higher,bending strength 2 times higher, and static loading strength 33.6percent higher than those of the races made of high-quality alloy steelof electroslag refining 1 percent carbon, 1.5 percent chromium, 0.6percent silicon, 1.5 manganese, and having a uniform hardness of 58 62HRC throughout their section. Besides, the fatigue strength of theproposed races with an artificially applied stress conwithout the stressconcentration whereas the fatigue strength of the through-hardened raceswith an identical stress concentration has decreased by 43 percent.

Strength characteristics of the inner race of a roller bearing forrailway car axle boxes determined by contact, fatigue and staticstrength tests Steel Type of Static Contact Max. breaking heatbreakstrength load under retreating (hours of peated bending ment loadoperation stress (test on stand basis 2 milunder 400% lion cycles)overload without with are before stress tificial contact concentstressfailure) rations concentration (pin-point burn) T hours T T proposedsteel surface harden- 40 1300 14 12 with definite ing after upper andlowthrough inducor hardenabiltion heating ity limits, with intensivecontaining cooling by C-- l .0%, stream of Cr0.42%, water, temper-Si0,22%, ing at C.

Mn0.20% surface hardness 62-64 HRC, depth of martensite layer 3 mm, corehardness 38 HRC Steel used at Hardening present After through C-0.95%,heating in Cr 1 .44%, furnace follow- Si0.57%, ed by oil Mn l .04%quenching.

after electro- Tempering at slag refining C. Hardness throughout entiresection 60-62 HRC We claim:

1. An antifriction bearing comprising: inner and outer races; rollingelements located between said races; said races and rolling elementshaving a uniform chemical composition of steel throughout their volumeand containing 0.8-1.2 percent carbon, the hardenability of said steelbeing confined at the upper and lower limits so as to ensure thefollowing relation:

where S wall thickness of said race or the diameter of the rollingelements, such as a ball or roller; and

d critical diameter, which is the diameter of a cylindrical specimenmade of said steel hardened by through-heating to the hardeningtemperature and by rapid cooling, such as for example water quenching,until it attains a hardness in the center thereof of 55 Rockwell C; andhaving a hardened layer of 58-65 Rockwell C hardness at least on therolling surfaces thereof, the depth of said layer being 0.1-0.3 of thewall thickness of said races or of the diameter of said rollingelements, and a core hardened to 30-45 Rockwell C hardness. 2. Anantifriction bearing according to claim 1 hardened all over.

wherein said races and rolling elements are made of steel containing0.9-1.1 percent carbon, 0.4-0.6 percent chromium, not over 0.1 percentsilicon and 0.1-0.3 manganese.

2. An antifriction bearing according to claim 1 wherein said races androlling elements are surface-hardened all over.
 3. An antifrictionbearing according to claim 1 wherein said races and rolling elements aremade of steel containing 0.9- 1.1 percenT carbon, 0.3- 0.5 percentchromium, 0.1- 0.3 percent silicon and 0.1- 0.3 percent manganese.
 4. Anantifriction bearing according to claim 1 wherein said races and rollingelements are made of steel containing 0.9- 1.1 percent carbon, 0.4- 0.6percent chromium, not over 0.1 percent silicon and 0.1- 0.3 manganese.